In numerous applications of devices in the medical field, it may be necessary or desirable to create a fluid-tight seal between structural components. For many medical devices, creating such as seal is manifestly critical to the safety and reliability of the devices. For example, it is often important for medical devices to incorporate a mechanism to prevent liquid or gasses, including air, from contacting certain device elements, entering the body through the device, seeping in, such as where suction pressure may be diluted, or leaking out of the device, such as where suction pressure may be lost.
In some particular applications, an intracorporeal device having rotational components is employed for therapeutic and/or diagnostic procedures. For example, devices to remove obstructions, including partial or total occlusions or other lesions of various types, from a target site in the body, e.g. a blood vessel, using a rotating cutter assembly is well established treatment modality in interventional cardiology. Numerous methods and devices have been conceived and developed.
Atherectomy or thrombectomy devices are often used for treatment of arterial occlusions. Atherosclerosis is a condition arising from the deposition of fat-like matter, i.e. plaque, on the walls of blood vessels. As a result of accumulated obstructions, blood flow becomes restricted or blocked, creating health risks, including coronary artery disease, angina and heart attacks. Most methods of using atherectomy and thrombectomy devices involve placement of a guiding catheter into the body and insertion of a guidewire, over which an operating head is guided to a target site where an occlusion is located within a blood vessel. However, devices that do not employ guidewires are also possible. A catheter surrounds a drive shaft to effectively isolate the rotating elements of the device from direct contact with any healthy body matter, e.g. tissue. The drive shaft is coupled to the operating head that is advanced, and in some devices, rotated to cut or ablate the obstruction and to restore or improve blood flow in the vessel.
It is important for atherectomy or thrombectomy procedures to include steps to collect dislodged particulates from accumulating in the body. Furthermore, findings have shown that stent deployment to treat Acute Coronary Sydrome (“ACS”) is often associated with plaque embolization in patients with ACS. See Circulation 2003; 107:2320-5. This heart damage increases the risk of long-term adverse clinical outcomes. In another example, kidneys are known to be very susceptible to blockage if embolisms occur in a renal artery during renal interventions. In the case of treatment of deep vein thrombosis, complications also occur if a clot breaks off and travels in the bloodstream to the lungs.
Some current devices employ filter systems to catch loosened debris. However, filter systems may allow small particles to pass and may be poorly positioned against a vessel wall. Other current devices use aspiration as an effective means to suction away embolic particulates that have been extracted from the body and provide embolic protection. However, it is important for the aspiration to be consistently maintained and provided at high rate. Therefore, a tight seal must be provided so that aspiration is not lost through cracks in the joint between device components. Moreover, the seal must prevent air from getting into the aspiration area and competing with aspiration for space. Accordingly, specific interest of the present invention is in maintaining fluid-tight seals which are necessary for the proper operation of an atherectomy device.
Regardless of the particular application, problems which must be overcome to establish a fluid-tight seal are particularly difficult when the seal is required between components that move relative to each other. For example, particles of matter that have been excised along with blood are often forced to enter a catheter and, so, fluid-tight seals are necessary to prevent the loss of blood through the gaps where the catheter ends and a rotating drive shaft continues to engage a motor. A sealing assembly may be required to seal the drive shaft and the catheter that encloses the drive shaft. In practice, a connector of catheter components and associated joints in catheter systems are prone to leaks because the catheter area may be under pressure during its operation.
During operation of an aspirating catheter system, there are often zones of substantially different pressures within the catheter or between the catheter and the body. The pressure difference may result in leakage of air, blood, or other gas or liquid. For example, rotation of components of the device, such as a drive shaft, may produce high rotational forces within the catheter system. Catheters with rotational drive systems are particularly problematic to seal against different zones of pressure, as in the case of a drive shaft that provides a lumen for a guidewire to translate from a zone of atmospheric pressure to zones of body pressure or zones of very low pressure. At a junction formed where the guidewire exits out the proximal end of the drive shaft, air may seep into the lumen. The decreasing pressure differential from the proximal end to the distal end of the drive shaft encourages invading air to travel along the length of the device and into the body. To address such problems, a seal is typically positioned at the drive shaft's proximal terminal end.
One conventional method for sealing a conduit in proximity to a drive shaft involves the use of an O-ring to surround the drive shaft. However, where the drive shaft rotates at a high rate, contact between the O-ring and the drive shaft often causes frictional heating, which may be destructive to the seal. An O-ring sealing the outside of a drive shaft also has no accommodation for sealing the lumen between the drive shaft and a guidewire.
Furthermore, some other current sealing mechanisms use a bushing around the drive shaft to seal it. But these bushing systems require close and precise tolerance between the outer surface of the drive shaft and the opening of the surrounding bushing. Both the drive shaft and the bushing must be machined to have very accurate dimensions. Also, with the bushing-type seal, the drive shaft needs to be smoothly finished in order to bear closely against the bushing. See, for example, U.S. Pat. No. 4,591,355. The machining process for such as sealing element is complex.
Moreover, current sealing mechanisms do little to seal drive shafts that are not solid shafts. Coiled wire drive shafts have gaps between the coils that may permit leakage. Nor are such sealing mechanisms effective to seal an inner channel in a drive shaft that is used for a guidewire.
It is therefore desirable to provide simple, effective seal for a torque tube and that creates no friction as a torque tube rotates. The seal should be able to prevent air from seeping into a catheter and diluting efficient aspiration through the system. It would be desirable for the seal to be relatively easy to manufacture, durable, and comparatively cost-effective. The present invention fulfills these needs and provides further related advantages.